1. Field of the Invention
The present invention relates to a display device for a vehicle which is useful in a head-up display or the like for a vehicle.
2. Description of the Related Art
As a display device for a vehicle, a HUD (Head-up display) device having a high visibility is sometimes employed in order to cause the driver to promptly recognize, for example, information which has a small information amount, but which has a high degree of urgency.
In a head-up display for a vehicle, a light image including visible information which is displayed on a display in the main unit of a display device is guided to the front of a windshield (front glass) of a vehicle, and projected to the windshield. When the driver sees the front in a usual driving position, the driver sees the visible information projected by the head-up display together with the landscape ahead which can be seen through the windshield. The visible information which is viewed by the driver is imaged as a virtual image in front of the surface of the windshield. While driving, therefore, the driver can simultaneously view both the landscape ahead and the display contents of the head-up display without shifting the driver's viewpoint.
In such a head-up display device, the main unit of the display device is usually placed in an instrument panel of a vehicle. Then, light of visible information which is displayed on a display in the main unit of the display device is projected through an optical path including a reflective member such as a mirror, toward a projection area such as a windshield or a combiner, and a virtual image is formed in front as viewed from the position of the viewpoint of the driver.
JP-A-2008-268680 discloses a conventional technique related to a head-up display for a vehicle. In JP-A-2008-268680, light emitting diodes which function as a light source for illumination, a lens array, a wiring board, a trimming filter, a liquid crystal display element, a cold mirror, a concave mirror, and a diffusion member are disposed in a housing of the main unit of the display device.
In the display device disclosed in JP-A-2008-268680, visible information is displayed in the transmissive liquid crystal display element, the element is illuminated with white light of the light emitting diodes which are placed behind the element, a light image due to illumination light transmitted through the liquid crystal display element is guided toward a windshield of a vehicle via the cold mirror and the concave mirror.